Make the pushover structures opaque.

In order to enforce using the API to set fields, make the structures
opaque. This will help prevent struct field abuse from consumers of this
library.
Signed-off-by: Shawn Webb <shawn.webb@hardenedbsd.org>

libpushover/libpushover.c

@@ -34,6 +34,21 @@
 
 #include "libpushover.h"
 
+struct _pushover_ctx {
+	uint64_t	 psh_version;
+	char		*psh_token;
+	char		*psh_uri;
+};
+
+struct _pushover_message {
+	char			*psh_dest;
+	char			*psh_msg;
+	char			*psh_title;
+	char			*psh_device;
+	pushover_priority_t	 psh_priority;
+	uint64_t		 psh_flags;
+};
+
 static char *msg_to_str(pushover_ctx_t *, pushover_message_t *, CURL *);
 static size_t pushover_curl_write_data(void *, size_t, size_t, void *);
 
@@ -54,8 +69,10 @@ pushover_init_ctx(const char *token)
 		goto out;
 	}
 
-	if (token != NULL)
+	if (token != NULL) {
 		res->psh_token = strdup(token);
+		assert(res->psh_token != NULL);
+	}
 
 	res->psh_version = LIBPUSHOVER_VERSION;
 

libpushover/libpushover.h

@@ -13,6 +13,12 @@
 #define	PUSHOVER_FLAGS_NONE	0
 #define	PUSHOVER_FLAGS_ALLOC	1
 
+struct _pushover_ctx;
+struct _pushover_message;
+
+typedef struct _pushover_ctx pushover_ctx_t;
+typedef struct _pushover_message pushover_message_t;
+
 typedef enum _pushover_priority {
 	PSH_PRIO_NONE = -2,
 	PSH_PRIO_QUIET = -1,
@@ -21,21 +27,6 @@ typedef enum _pushover_priority {
 	PSH_PRIO_CONFIRM = 2
 } pushover_priority_t;
 
-typedef struct _pushover_ctx {
-	uint64_t	 psh_version;
-	char		*psh_token;
-	char		*psh_uri;
-} pushover_ctx_t;
-
-typedef struct _pushover_message {
-	char			*psh_dest;
-	char			*psh_msg;
-	char			*psh_title;
-	char			*psh_device;
-	pushover_priority_t	 psh_priority;
-	uint64_t		 psh_flags;
-} pushover_message_t;
-
 pushover_ctx_t *pushover_init_ctx(const char *);
 void pushover_free_ctx(pushover_ctx_t **);
 bool pushover_set_uri(pushover_ctx_t *, const char *);